Part 4 of Understanding Federal Tyranny examines the Legal Tender Act of 1862, the first Act under the Constitution to emit paper currencies and declare them a legal tender.
This audio examines two of the first three court cases to rule on the matter, as they all denied that the paper currency notes were a legal tender in the cases before the court (going so far as to say that the Constitution prohibited legal tender paper currencies).
The audio then examines next the Legal Tender Cases court ruling of 1871, which upheld paper currencies declared a tender, but only as a legal tender for the District of Columbia under Article I, Section 8, Clause 17 of the U.S. Constitution.